Additionally, there are a handful of related minor changes in this commit:
- `.travis.yml` has been tidied up a little.
- [45745] was incorrectly marking Travis jobs as passed when some PHPUnit runs failed.
- Add the `LOCAL_PHP_MEMCACHED` environment variable, for enabling Memcached.
- Add the `env:pull` NPM script, for refreshing Docker images.
See #47767.
git-svn-id: https://develop.svn.wordpress.org/trunk@45762 602fd350-edb4-49c9-b593-d223f7449a82